We are focusing on larger-order issues concerning mitochondrial structure and function relationships, which range from localizing cytochrome oxidase and other electron transport proteins in cristae to understanding the mitochondrial structural response to ischemia and anoxia. We are using tomographic reconstructions performed on the IVEM of mitochondria in 0.5 urn thick sections. The first issue that we had to investigate was which structural features would be visible in 3-D reconstructions and at what resolution. We chose to start be reconstructing mitochondria from neural tissue since different kinds of mitochondna are present in the same tissue. Reconstructions of dendritic and axonal mitochondria show clearly demarcated membranes at a resolution of about 10 nm. hence, it appears that quantitative information can be obtained about mitochondrial structure in situ. The two completed reconstructions underscore the capability of tomography for examining in detail relatively large, complex structures. Continuing work involves additional investigation into the observed structural differences between dendritic and axonal mitochondria. A second pursuit will be a study of differences in mitochondrial architecture of ischemic and recovering animals. This work is a new collaboration with Justin Zivin, in the department of Neurosciences, who has developed models of animals at various stages of recovery after an ischemic episode.